1. Field of the Invention
This invention relates to a digital camera and a method for controlling the exposure of the digital camera.
2. Description of the Related Art
As it is known, the photographing lens of a digital camera focuses an optical image onto a CCD (charge coupled device), which then photoelectrically converts the optical image into an electric signal. The generated electric signal is subjected to predetermined image processing, so that the photographed image is recorded as digital image data in a recording medium, such as a memory card. The recorded digital image is displayed on a display (e.g., an LCD panel).
A typical digital camera also has an exposure control system. A conventional exposure control system for a digital camera computes an appropriate exposure time based on the image data which was generated from the object image focussed onto the image pick-up device (e.g., the CCD).
In general, the diaphragm of a digital camera is of a fixed type. Accordingly, the exposure time, or the charge accumulation time of the CCD, which corresponds to the shutter speed of the digital camera is adjusted to obtain the optimum quantity of exposure.
However, with the conventional exposure control system for a digital camera, an exposure control value must be calculated for each photographing action by the arithmetic operation loop. If the object is photographed successively at a high speed to produce sequence photographs, the computation time (or the arithmetic operation time) for producing the appropriate exposure control value becomes longer than the photographing interval. If a priority is given to the high-speed successive photographing without adjusting the exposure value the quality of the resultant images is deteriorated due to inappropriate exposure because the photographing conditions cannot follow the change in the brightness of the object.
Another technique for controlling the exposure time is to provide a light-receiving device, such as a photoconductive cell and a photodiode, for exclusive use in exposure control. The exposure time is controlled in accordance with the brightness information of the object obtained from the light-receiving device. However, because the exclusive light-receiving device is required other than the CCD, the number of components increases, the size of the camera becomes larger and the cost of manufacturing the digital camera also increases.